From: Pietro Borrello borrello@diag.uniroma1.it

commit 7c4a5b89a0b5a57a64b601775b296abf77a9fe97 upstream.

Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()") removed any path which could make pick_next_rt_entity() return NULL. However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of pick_next_rt_entity()) still checks the error condition, which can never happen, since list_entry() never returns NULL. Remove the BUG_ON check, and instead emit a warning in the only possible error condition here: the queue being empty which should never happen.

Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()") Signed-off-by: Pietro Borrello borrello@diag.uniroma1.it Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Phil Auld pauld@redhat.com Reviewed-by: Steven Rostedt (Google) rostedt@goodmis.org Link: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v3-1-b1a71bd1... Signed-off-by: Sasha Levin sashal@kernel.org [Srish: Fixes CVE-2023-1077: sched/rt: pick_next_rt_entity(): check list_entry An insufficient list empty checking in pick_next_rt_entity(). The _pick_next_task_rt() checks pick_next_rt_entity() returns NULL or not but pick_next_rt_entity() never returns NULL. So, even if the list is empty, _pick_next_task_rt() continues its process.] Signed-off-by: Srish Srinivasan ssrish@vmware.com --- kernel/sched/rt.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 9c6c3572b..394c66442 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1522,6 +1522,8 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq, BUG_ON(idx >= MAX_RT_PRIO);

queue = array->queue + idx; + if (SCHED_WARN_ON(list_empty(queue))) + return NULL; next = list_entry(queue->next, struct sched_rt_entity, run_list);

return next; @@ -1535,7 +1537,8 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)

do { rt_se = pick_next_rt_entity(rq, rt_rq); - BUG_ON(!rt_se); + if (unlikely(!rt_se)) + return NULL; rt_rq = group_rt_rq(rt_se); } while (rt_rq);

-- 2.35.6